The present invention relates generally to non-volatile memory devices and in particular the present invention relates to a synchronous non-volatile flash memory.
Memory devices are typically provided as internal storage areas in the computer. The term memory identifies data storage that comes in the form of integrated circuit chips. There are several different types of memory. One type is RAM (random-access memory). This is typically used as main memory in a computer environment. RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost.
Computers almost always contain a small amount of read-only memory (ROM) that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to. An EEPROM (electrically erasable programmable read-only memory) is a special type non-volatile ROM that can be erased by exposing it to an electrical charge. Like other types of ROM, EEPROM is traditionally not as fast as RAM. EEPROM comprise a large number of memory cells having electrically isolated gates (floating gates). Data is stored in the memory cells in the form of charge on the floating gates. Charge is transported to or removed from the floating gates by programming and erase operations, respectively.
Yet another type of non-volatile memory is a Flash memory. A Flash memory is a type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCS have their BIOS stored on a flash memory chip so that it can easily be updated if necessary. Such a BIOS is sometimes called a flash BIOS. Flash memory is also popular in modems because it enables the modem manufacturer to support new protocols as they become standardized.
A typical Flash memory comprises a memory array that includes a large number of memory cells arranged in row and column fashion. Each of the memory cells includes a floating gate field-effect transistor capable of holding a charge. The cells are usually grouped into blocks. Each of the cells within a block can be electrically programmed in a random basis by charging the floating gate. The charge can be removed from the floating gate by a block erase operation. The data in a cell is determined by the presence or absence of the charge in the floating gate.
A synchronous DRAM (SDRAM) is a type of DRAM that can run at much higher clock speeds than conventional DRAM memory. SDRAM synchronizes itself with a CPU""s bus and is capable of running at 100 MHZ, about three times faster than conventional FPM (Fast Page Mode) RAM, and about twice as fast EDO (Extended Data Output) DRAM and BEDO (Burst Extended Data Output) DRAM. SDRAM""s can be accessed quickly, but are volatile. Many computer systems are designed to operate using SDRAM, but would benefit from non-volatile memory.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a non-volatile memory device that can operate in a manner similar to SDRAM operation.
The above-mentioned problems with memory devices and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
A synchronous non-volatile memory device in one embodiment comprises an array of non-volatile memory cells arranged in addressable rows and columns, a column address counter circuit, a data mask signal input to receive a data mask signal, and control circuitry coupled to the array to store a data packet received on data connections to the array. The control circuitry writes a first data packet coincident with an inactive data mask signal and received after an externally provided row active command. In another embodiment, the synchronous non-volatile memory device further comprises an internal column address counter circuit. The internal column address counter circuit latches a start column address received with a first write command and advances the start column address in response to subsequent write commands. The synchronous non-volatile memory device can include a non volatile mode register to store data indicating a memory burst length.
A method of writing to a synchronous non-volatile memory device is provided in another embodiment. The method comprises initiating a burst write operation, receiving an active row command, receiving a plurality of data packets following the active row command, and using an externally provided data mask signal to prevent one or more of the plurality of data packets from being written to the synchronous non-volatile memory device.
Another method of writing a plurality of X data packets to a synchronous non-volatile memory device comprises receiving X data sequences each containing the X data packets, and writing one of the X data packets during each of the X data sequences. A data mask signal can be used to prevent Xxe2x88x921 of the X data packets from being written on the Xth data sequence. Each of the X data sequences can each contain a row active command preceding the X data packets. Also, an initial column address can be provided coincident with a first one of the X data sequences, and the synchronous non-volatile memory device can advance the initial column address on subsequent X data sequences.
In yet another embodiment, a method of operating a memory system comprises transmitting a plurality of command and data packet sequences from a processor to a synchronous non-volatile memory device. Each of the plurality of command sequences comprises a command to load a mode register, a row active command and a plurality of write commands. One of a plurality of data packets is written on each of the data packet sequences to an array of the synchronous non-volatile memory device. A data mask signal provided by the processor prevents more than one of the plurality of data packets from being written on each of the data packet sequences.